The present invention refers to sintered abrasive grain agglomerates with a portion of aluminum oxide of at least 80% by weight, an average primary particle diameter of less than 5 μm, an substantially spherical outer shape, with a portion of pores of at least 15% by volume and a mean agglomerate size in the range between 5 μm to 500 μm.
The present invention also refers to a process for producing sintered abrasive grain agglomerates as well as their use as lapping agents for the production of organically or inorganically bonded abrasive bodies, for the production of abradants used on a substrate as well as in wear protection layers.
Abrasive grain agglomerates are known in many variations for some length of time and normally are used in connection with bonded abradants such as for example abrasive disks, or abradants on substrates such as for example abrading belts. Abrasive grain agglomerates are normally constructed from single abrasive grains, the primary particles that are bonded together by means of a binder into a abrasive grain agglomerate. As binding agents either organic or inorganic binders can be utilized, wherein phenol resins are oftentimes used as organic binders, while glass-like or ceramic binders are used as inorganic bonding agents.
The big advantage of abrasive grain agglomerates is in fact that finely grained abradants can be utilized as primary particles from which an agglomerate grain is then formed which, as compared to a single grain of comparable size, exhibits an entirely different wearing mechanism during the abrading- and wearing process. A single grain of comparable size, according to pressure conditions, either dulls during the abrading process, or it will be destroyed. In contrast, with the abrasive grain agglomerate, the abrading conditions are selected so that single grains break out from the compound, such that new cutting edges are constantly formed which lend the agglomerate grain a long life expectancy while showing a cool smoothness and a homogenously polished section. A further advantage of the abrasive grain agglomerate is that in this manner, the finest abrasive grains can be utilized for abrading processes and abrading tools, for which they are otherwise not suited due to their small grain size.
In DE 103 92 532 B4, abrasive grain agglomerates are described which comprise a multitude of abrasive grains that are held together with a bonding agent, wherein the bonding material has a melting temperature in the range of 500° C. to 1400° C. In DE 103 92 532 B4, a method for the production of such abrasive grain agglomerates is also described, wherein the abrasive grains are mixed with a bonding agent and subsequently are subjected to a heat treatment in a revolving furnace in a temperature range of 145° C. to 1300° C. The agglomerates that are thus obtained have a total porosity between 35% by volume and 80% of volume, wherein at least 30% by volume of the pores are interconnected. In this process, elongated agglomerates are formed that have a length ratio of length to cross section of at least 5:1. As a bonding agent, glass-like bonding materials, vitrified materials, ceramic materials, inorganic bonding agents, organic bonding agents and combinations of these are utilized. The so obtained abrasive grain agglomerates should be most of all used in bonded abradants in order to control the properties of porosity and the porosity in the form of a permeable and interconnected porosity.
In DE 10 2005 007 661 A1, abrasive bodies are described that are formed and bonded together by means of a bonding agent into abrasive grains in material union and exhibiting at least approximately a spherical outer shape, wherein the abrasive grains have a porosity of at least 35% by volume. These abrasive grain agglomerates are formed from single abrasive grains, with a particle size in the range between of 0.05 μm and 150 μm, which are then joined with abrasive grain agglomerates with an outer diameter in the range of 10 μm and 150 μm. In the abrading tools, these agglomerates are utilized that are graded narrowly, as quasi constant grainings. Binders that are preferred are organic binders, such as for example phenol resins, polyurethane, epoxide resins, urea resin and poly vinyl butyral. These agglomerate abrasive grains are meant especially for utilization with abradants on substrates where they are used for very fine abrasive treatment of work piece surfaces.
Although the production of abrasive grain agglomerates is in principle relatively uncomplicated and is based simply on mixing together single abrasive grains with a bonding agent to then form an abrasive grain agglomerate that is subsequently heat treated, in practice, technical process problems occur in nearly all known methods for obtaining homogenous and evenly formed agglomerates with respect to the size of the agglomerates, as also with respect to the shape of the agglomerates and the composition of the agglomerates. These problems originate mostly when very fine abrasive grains of medium size of a few microns are mixed with a binder and subsequently are heat treated.
When utilizing solid binders the problem might already be based on the fact that the size of the particles of the binding agent is coarser than those of the abrasive grains to be bonded and makes any homogenous mixing harder. When using liquid binders or those diluted with solvents, the problem is oftentimes that the abrasive grains lump together, whereby a homogenous distribution of the bonding agent in the abrasive grain granulation is prevented and the production of a homogenous product made more difficult.
A further technical problem of the method, in particular when utilizing organic binders is the contamination of the apparatus used, as the mixtures of binder and abrasive grains tends to conglutinate at the walls of the apparatus. Therefore, this leads, in particular when changing products, to high cleaning maintenance, and when producing agglomerate grains, since the desired abrasive grain agglomerate of abrasive grains composed of a narrow grain size has to be realized. Such contamination with coarser grains would lead to considerable problems, for example, in abrading operations where it mostly concerns the superfine treatment of work piece surfaces, such as, for example, the treatment of decorative lacquer layers could lead to considerable problems if such contamination with coarse grains caused scratches, which subsequently would needed to be removed, if even possible, with a considerable amount of work. With bonding agents, aside from them causing contamination in the apparatus, environmental protection is also a concern, since the use of organic solvents or binders are mostly associated with annoyances such as bad smell as well as health risks.
Thus, as a basis for solving this problem, the object of the present invention was to provide abrasive grain agglomerates that do not suffer from the drawbacks of the prior art.